The present invention relates to character recognition apparatus and, more particularly, to apparatus for producing a binary signal to be used for character recognition responsive to a character signal which is obtained by an optical scanner or the like.
In a character recognition apparatus, generally speaking, a character signal obtained from an optical scanner is sliced at a suitable threshold level (slice level) to produce a binary signal. Character recognition is conducted by making use of that binary signal. However, the suitable slice level varies with the density and size of the characters written on a document and/or with the background of the document. As a result, a failure in determining the suitable slice level leads to a reduction in the recognition percentage or to an erroneous recognition.
In a first prior art procedure, there is a method of dynamically determining a slice level. An analog character signal obtained from a scanner is converted into a digital character signal at multiple levels, e.g., four to sixteen levels. An average level of a background in a small area surrounding a point to be made binary is determined as the slice level. In a second prior art procedure, a plurality of binary signals are produced in accordance with a plurality of different slice levels. Recognition is repeated in response to respective binary signals, to seek an appropriate recognized conclusion. Since the slice levels are determined in a respective microscopic area, according to the first method, a pattern of the background may be erroneously taken up as the character pattern, when a reflection rate of the background varies in a complex manner. The second method is superior to the first in that the character recognitions are conducted at the various slice levels. The final result is outputted, while compensating for the defect of the first method. However, since the recognitions have to be repeated at the various slice levels, the second method has a defect because a long time period is required for the recognitions. On the other hand, for high speed operations, it is conceivable to use a plurality of recognition units. However, this raises the cost for hardware.